Mattress innersprings, or simply “innersprings”, made of matrices or arrays of a plurality of wire form springs or coils, have long been used as the reflexive core of a mattress padding and upholstery is arranged and attached around the innerspring. Innersprings made of formed steel wire are mass produced by machinery which forms the coils from steel wire stock and interconnects or laces the coils together in the matrix array. With such machinery, design attributes of innersprings can be selected and modified, from the gauge of the wire, the coil design or combinations of designs, coil orientation relative to adjacent coils in the matrix array, and the manner of interconnection or lacing of the coils.
Mattresses and other types of cushions have for decades been constructed to be “double-sided” or in other words symmetrical in cross-section, wherein the configuration and arrangement of materials and components is identical on each side. Double-sided symmetrical construction enables flipping of the cushion or mattress to obtain the same support characteristics on a fresh uncompressed side. It was long held that this was necessary to allow compressed layers of padding, particularly natural materials such as cotton batting or fowl feathers, to decompress while the opposite side was used as the support side. But with the advent of improved materials for the padding layers, including foam materials with excellent resilience which promptly return to an uncompressed or substantially uncompressed state, the padded support side does not require a prolonged recovery period as was provided by flipping to an performance for the life of the product. This has led to the recent development of “one-sided” mattresses, designed and constructed to have only one support permanent support side or surface, with an opposite side designed for permanent support by and contact with the top side of a box spring or foundation. One-sided or “no-flip” mattresses are thus designed to concentrate essentially all of the support and comfort features at or near the single support side, with the opposite or bottom side serving only as a platform for support by a foundation. The amount and quality of padding and other filling materials at or near the support side is therefore dramatically greater than at the opposite bottom side.
A recent trend in mattress design is the one-sided “no flip” mattresses, having only one surface or weight-bearing side. In one-sided mattresses, padding is eliminated from the bottom side an augmented on the support side. However, despite this radical change in the padding placement, the innerspring design has not been changed or designed for one-sided support performance. Instead, the construction of one-sided mattresses has continued to use conventional innersprings, which, due to their symmetrical construction resulting from the use of generally symmetrical coils as manufactured by coil production, have two sides (as defined by the coils ends) which provide reflective support. In this respect, in a one-sided mattress made with a conventional innerspring, there is a substantial amount of wire material and structure on the bottom side of the innerspring which is excessive and not required for adequate or optimal performance of the single support surface.
Among the many design attributes of wire form innersprings, the height and stiffness of the individual coil springs are especially important. The overall height of a mattress is dictated in part by the height of the coils, and tall coils such as in the 5.5 inch-8.0 inch range are desirable for American style high profile mattresses. High height coils and innersprings present a greater engineering challenge to maintain adequate stiffness. In helical shaped coils, stiffness generally decreases with height, which is achieved by forming a greater number of helical turns of wire in the body of the coil. The smaller helical angle between the more numerous turns of the coil requires less force for compression. Although this provides a softer support structure, it can be too soft to provide adequate and long-lasting support in a one-sided mattress. Also, when the number of helical turns is increased symmetrically about the length of the coil, this adds wire at the bottom end of the coil where there is no direct load applied in a one-sided mattress. The stiffness of coils can be increased by using heavier gauge wire, but this adds significantly to weight and material costs. Therefore, simply increasing the number of coil turns in the coils of an innerspring is not a practical solution to creating a high height or high profile innerspring for use in a one-sided mattress.
A primary factor in innerspring design is material cost, namely that of steel wire. Although heavier gauge wire can be used to increase stiffness, as mentioned this increases material and handling costs. Also, heavier gauge wire induces a greater amount of wear on the wire forming equipment used to manufacture innersprings. A coil design which has adequate or augmented height and stiffness, and which is configured to have one of many weight-bearing end and which requires a lesser amount of material than conventional symmetrical coils would be desirable.
In this respect, in a one-sided mattress with a conventional innerspring, there is a substantial amount of material and structure on the bottom side of the innersprings which is excessive and not required for adequate or optimal performance. Among the many design attributes of a wire form innerspring, height and stiffness of especially important. The overall height of a mattress is dictated in part by the height of the coils, and tall coils such as in the 6.5-7.5 in range are desirable for American style tall profile mattresses. High height coils and innersprings present a greater engineering challenge to maintain adequate stiffness, which generally decreases with height as achieved by a greater number of helical trims of wire per coil.
Another factor in innerspring design is material cost, namely that of steel wire. Although heavier gauge wire can be used to increase stiffness, this of course increases the cost. Also, heavier gauge wire induces a greater amount of wear on the wire forming equipment. A coil design which has adequate height and stiffness, and which is configured to have one of many weight-bearing end and which requires a lesser amount of material than conventional symmetrical coils would be desirable.